A spectrum of a necrotic cell showed that all the infrared bands are much broader than those observed with viable cells. The most striking difference was the appearance of a narrow band that was assigned to carbonyl ester groups. In the future, we hope to extend this infrared microspectroscopic technique to monitoring changes in the intracellular localization of chemical compounds occurring inside individual cells during various biological events such as mitosis, drug uptake, receptor activation, endocytosis, and apoptosis.